The invention relates to a fastening element for attaching insulating strips or plates and possibly additional sealing strips to a solid substructure, consisting of a screw which is provided with a thread over at least a portion of the length of its shaft and has a screw head, and a large-area washer having a tubular extension, in which the extension of the washer has, at least over a large portion of its length, an internal cross-section sufficiently large for the rotatable reception and for the axial displacement of the screw head and which is narrowed at its end region remote from the washer to permit passage of the screw""s shaft. The invention relates further to a method of attaching insulating strips or plates and possibly other additional sealing strips or bituminous underlayers to a solid substructure of thin concrete by means of a fastening element which consists of a screw and a large-area washer having a tubular extension.
Solutions are indeed known, in which the fastener is telescopically slidable within the tubular extension, so that a variation in overall length can be achieved. However, such a construction is not desirable, especially for a roof structure in which the large-area washer is to be pressed against the top-most sealing strip.
Applications for attaching insulating and sealing strips to a substructure of thin concrete or other materials, e.g. sheet metal and the like, also exist in new construction, when a relatively thick insulating strip is used. In such a case, too, the overall length of the fastening element formed by the fastener itself and the tubular extension of the large-area washer, desirably enables the compensation for different overall thicknesses of the materials to be attached, over a relatively wide range. Especially for cases in which such compensation is desired, but the known telescope-like configuration of relatively slidable fastener and tubular extension is not suitable, there were heretofore no adequate solutions.
Therefore, the object of the present invention is to provide a fastening element and a method of the kind described at the outset, by which large attachment distances can be bridged by the use of a fastener and a large-area washer with a tubular extension, which nevertheless enables the adequately forceful pressing of the large-area washer against the topmost sealing or insulating strip.
This is accomplished in accordance with the invention by making the outer diameter of the screw shaft thread greater than the free pass-through opening of the narrowed region of the tubular extension, whereby the screw is in operative engagement with the narrowed region of the tubular extension through mutual threaded engagement, or else can be brought into such engagement by rotating the screw into the pass-through opening.
By these techniques embodying the invention, the washer with its tubular extension can be pushed into a correspondingly preformed hole in the entire structure, using a washer with a tubular extension of the available length. During screwing of the fastener into the substructure, the same simultaneously enters into operative engagement with the tubular extension over an appropriate thread section, so that telescope-like axial displacement between fastener and tubular extension is no longer possible. Thus the fastener and the washer with its tubular extension form an axially stable attaching element. However, because the fastener and the narrowed region of the tubular extension are in mutual threaded engagement, the washer together with its tubular extension can subsequently still be rotatedxe2x80x94if that appears to be necessaryxe2x80x94whereby, for example, the force pressing the large-area washer against the top side of the insulating or sealing strip can be increased. That is, through rotation of the large-area washer, the latter is drawn axially further toward the interior, depending upon the thread pitch of the fastener, or else the applied pressure can be reduced by reverse rotation of the washer and with it the tubular extension, if the compressing is too strong.
An advantageous embodiment provides that the screw is provided with a thread over at least a substantial portion of the length of its shaft. By so doing, a large region can be used as the needed overall length of the attaching element, because the fastener can extend more or less far into the tubular extension of the washer. What is important is only that a threaded region of the fastener is in threaded engagement with the narrowed region at the free end of the tubular extension. For that reason, for greatest possible utilization of the length of the fastener and of the length of the tubular extension, it is desirable that the screw be provided with a thread over the entire length of the shaft.
A further advantageous construction consists in providing two differently formed thread sections on the shaft of the screw. This permits accommodating the possibility that, in the substructure to which the entire structure is to be ultimately attached, there can be provided a thread which is suitable for the substructure and the optimum thread configuration can be provided in the region of threaded engagement between the screw and the narrowed portion of the tubular extension.
In this regard, it is preferred that the two thread sections on the screw shaft have different diameters but the same thread pitch. To achieve even better engagement, it may be appropriate to penetrate the substructure using a smaller outer diameter. This also makes it possible, for example, that the first thread section of smaller diameter does not need to be threaded through the narrowed portion of the tubular extension. This is desirable especially for pre-mounting the fastener in the tubular extension.
For special substructures, it may be desirable to make the smaller diameter thread section at the free end of the screw shaft double-threaded. This also makes it possible to make the double-threaded part of the threaded section with threads having different outer diameters. Such a structural configuration is especially advantageous for direct application to concrete.
A further desirable embodiment provides that, if there are two thread sections of different diameters, the pass-through opening of the narrowed region of the tubular extension approximately equals the outer diameter of that section of the shaft having the smaller diameter thread. This enables initial centering of the free end of the fastener in the narrowed region during pre-mounting, after which an inseparable pre-mounting becomes possible by means of one or more rotations.
In the tubular extension, the narrowed region of the pass-through opening can be simply cylindrical. By so doing, as a practical matter, a thread is cut or pressed into a corresponding core-boring of the inserted fastener. In principle, an appropriate thread-boring can also be made in advance in the region of the pass-through opening, although this involves substantially higher manufacturing costs for the tubular extension.
The pass-through opening in the narrowed region of the tubular extension can also be non-round in cross-section, or else provided on its wall with ribs, protrusions, burls, grooves, or the like. In that version, there sometimes exists no circumferentially closed mutual thread engagement, but that is also not necessary for certain applications. What must be assured is only that mutual axial displacement between fastener and tubular extension results from mutual relative rotation with an advance corresponding to the thread engagement.
In the inventive method, it is proposed to first make, in the structure formed by insulating strips, or plates, sealing strips and possibly additional layers, a hole substantially equal to the outer diameter of the tubular extension, then to make a hole in the concrete substructure which matches the thread of the screw, or of a hole in a plug for screw insertion. There the washer with its tubular extension and the screw are inserted and the screw is driven in to the expected penetration depth. In so doing, the screw forms a mating thread in the narrowed end region of the extension, or engages a thread previously formed therein. Finally, if stronger pressure of the washer against the top-most insulating strip is needed, the washer together with its tubular extension, which is in cooperative engagement with the screw, is rotated relative to the screw.
By this process, optimum fastening is obtained not only in restorations of existing roofing structures, but also in new construction. But especially in the renovation of a substructure whose thickness is not known in advance, the above-described fastening element used with the inventive process is especially desirable. Even the making of the first hole in the overall structure can already provide a kind of test hole, by means of which the overall thickness of the structure can be determined. Then, fastening elements can be used in which the length of the tubular extension and the length of the screw are coordinated. Also optimized is the ability to retroactively, i.e. after final setting of the fastener, to adjust the pressure of the washer by rotating it relative to the fastener.
A further desirable feature of the method is that the uppermost edge of the opening, which is defined in the washer by its tubular extension, can be brought into cooperative relationship by means of a drive tool. Required is only appropriate friction between the tool and the washer, in order to effect a rotation thereof, and with it a drawing-together, or a loosening.